The present invention relates to handle and interlock systems, and more particularly to an improved, defeatable handle assembly for cabinets enclosing electrical gear. The handle assembly to be described is usable in conjunction with a racking mechanism such as that shown in application Ser. No. 373,092 "Racking Mechanism for Motor Control Center or the like"--J. Kleinecke and T. Little, filed concurrently herewith.
Medium and high voltage switchgear and electrical control apparatus ae conventionally housed in sheet metal enclosures which not only provide a mounting for the main contactor assemblies and auxiliary apparatus and protect the apparatus from damage, but also serve to prevent unauthorized access to the energized electrical equipment therein. Since the equipment frequently includes high voltage members and exposed conductors, there is obviously danger of damage to equipment and injury to personnel if it is readily accessible. For this reason, cabinets which enclose such gear are frequently divided into high voltage and low-voltage sections. The low-voltage apparatus, including controls, meters and the like is housed in a first cabinet to which access may be gained by simply disengaging a latch and opening a door. The high voltage equipment, conventionally including a contactor and associated gear, is usually housed in a different compartment which is isolated by means of sheet metal partitions. Elaborate precautions are taken to assure that the high voltage compartment cannot be opened unintentionally, or by unauthorized individuals. Frequently either a rotatable or a lever-type handle is provided in conjunction with a racking mechanism, and the contactor assembly placed on a removable carriage. As described in application Ser. No. 373,092 referred to above, the racking mechanism engages the carriage and urges it into electrical contact with fixed bus bars of the like which are placed in the compartment. The racking mechanism is conventionally interlocked with the door assembly so that the mechanism cannot be racked, or brought into contact with energized bus bars, unless the cabinet is closed and secure. In this manner the assembly is only energized when the enclosure is closed.
It is conventional for the handle assembly to be interlocked with the racking mechanism and door assembly in such a manner that when the mechanism is racked, and the handle in its "on" position, the door may not be opened and access cannot be gained to the live equipment within. However, in some circumstances it may be necessary to open the compartment while the apparatus is energized. Owing to the hazard involved such access is restricted to authorized, skilled individuals who have the appropriate training and background to work on the system in its live state. Ordinarily provision for one or more padlocks is made so that only authorized individuals who have keys to the locks can open the compartment.
While in principle there are numerous mechanisms which can be adapted to use for racking, securing and interlocking the contactor and cabinet assembly, owing to the large mechanical forces involved and the size of the various mechanical elements it has been found difficult to provide an interlocking mechanism which operates easily to rack the contactor mechanism, is relatively economical and straight forward to manufacture, and is not unduly intricate. Further the mechanisms required for defeating the interlocking operation have frequently been cumbersome, expensive and complex and in some instances difficult to use. Accordingly, it will be appreciated that it would be highly desirable to provide an improved racking handle mechanism for an electrical enclosure which is straightforward in design, easily manipulated, and bearing a non- -obvious but easily accessible defeat mechanism.
Accordingly, it is an object of the present invention to provide an improved interlock handle and defeat system for an electrical equipment enclosure.
Another object is to provide an easily constructed handle mechanism for an electrical enclosure whose operation may be readily defeated by individuals who understand the operation of the system.
Yet another object is to provide a door interlock system and handle combination which is effective, difficult to overpower, and whose defeat mechanism is not immediately apparent to an operator.